1. Field of the Invention
The present invention relates to an image forming apparatus such as electro-photographic apparatus, printers, etc. for forming developing images on a belt-shaped photo-conductor by non-magnetic one-component contact developing devices or a two-component developing device.
2. Description of the Related Art
In recent years color image forming apparatus such as color multifunction peripheral (hereinafter abbreviated to MFP) with a color copying machine, a color printed or further, a facsimile function incorporated into one unit has been in wide use. In offices equipped with such color image forming apparatus, both of conventional monochrome image forming apparatus such as monochrome copying machines, printer, etc. and color image forming apparatus are installed in many cases. However, in order to further promote wide use of color image forming apparatus in the future, it is necessary to reduce a space required for installing a color image forming apparatus so that it can be used in small offices that have a limited space and the development of a practically usable image forming apparatus for color image forming having the performance equivalent to a conventional monochrome image forming apparatus in one unit is demanded.
As an image forming apparatus capable of forming color images, a color image forming apparatus to obtain a full color image by forming yellow (Y), magenta (M), cyan (C) and black (K) toner images in order on a photosensitive belt using non-magnetic one-component contact developing devices, and then superposing these toner images on the photosensitive belt or an intermediate transferring drum and collectively transferring them on a recording paper as disclosed on Japanese Laid-Open Patent Application No. Kai-Hei 6-138744 has been used widely. That is, in a color image forming apparatus, as plural developing devices are provided for respective toner colors and maintenance frequency of the developing devices will increase accordingly, non-magnetic one-component contact developing devices having high user maintainability are used for easy exchange of developing devices and toners by user.
However, a higher cost is required per image for the image forming using non-magnetic one-component contact developing devices and when such non-magnetic one-component contact developing devices are used for the monochrome image formation that consumes much black (K) toner only, a cost per image becomes higher than that of a conventional monochrome image forming apparatus and it becomes not economical.
So, the development of an image forming apparatus has been so far desired, which is equipped with a color image forming apparatus and a monochrome image forming apparatus in one unit and requires a small space for installation, with a priority given over maintainability in the color image formation and reduction of cost per image in the monochrome image forming and with the performance equivalent to that of a conventional monochrome image forming apparatus including economy as well as quality of image.
An object of this invention is to reduce a space for installing a color image forming apparatus and a monochrome image forming apparatus in offices.
Further, another object of this invention is to achieve the monochrome image formation at a cost nearly equal to an image forming cost of a conventional monochrome image forming apparatus using a color image forming apparatus equipped with the monochrome image forming function.
According to this invention, an image forming apparatus is provided. This image forming apparatus comprises: an image carrier that travels endlessly; plural supporting members supporting the image carrier so that it is able to travel; a latent image forming portion for forming a latent image on the image carrier; a first developing device having first developing members that contact the image carrier after passing the latent image forming portion and form a developed image by supplying developers to the latent image; and a second developing device having a second developing member that is facing the image carrier after passing the latent image forming portion with a prescribed gap and forming a developed image by supplying developers to the latent image.
Further, according to this invention, an image forming apparatus is provided. This image forming apparatus comprises: a belt-shaped photo-conductor; plural roller members supporting the photo-conductor so that it is able to travel; a latent image forming portion for forming a latent image on the photo-conductor; a non-magnetic one-component contact developing device having a first developing member for forming a developing image by supplying non-magnetic one-component developer to the latent image by contacting the photo-conductor after passing the latent image forming portion; and a two-component developing device having a second developing member that is facing to the photo-conductor at a prescribed gap in an area supported by one of the plural rollers after passing the latent image forming portion for forming a developing image by supplying two-component developer to the latent image.